Indirect heater

ABSTRACT

The heater includes a vessel containing a heat transfer fluid and a fire tube located adjacent the bottom to heat the heat transfer fluid. The fluid to be heated flows through a coil located in the vessel above the fire tube but submerged in the heat transfer fluid. The coil encircles two void boxes that occupy a substantial portion of the space in the vessel and reduce the volume of heat transfer fluid required to fill the vessel to a level above the boxes and the coil. The void boxes are spaced apart and positioned relative to the fire tube to cause the heat transfer fluid to flow upwardly between the boxes and downwardly past the coil between the boxes and the walls of the vessel due to the heat convection currents produced by the thermosyphonic effect. When the fluid being heated is a gas and the pressure of the gas is to be reduced, a choke is located in the coil adjacent its outlet to reduce the pressure after the gas has been heated. This reduces the condensation of liquids and the possibility of their freezing due to the reduction in temperature resulting from the pressure drop across the choke.

United States Patent [72] Inventor Lawrence J. Sullivan Odessa, Tex. [21] Appl. No. 836,001 221 Filed June 24, 1969 [45] Patented Sept. 7, 1971 [7 3] Assignee Sivalls Tanks, Inc.

1 Odessa, Tex.

[54] INDIRECT HEATER 3 Claims, 5 Drawing Figs.

[52] US. Cl

122/501,126/366,165/106,165/108, 219/326 [51] Int. Cl F17c 9/02 [50] Field 01 Search 165/104, 106, 107, 108,62/52; 122/5()1,502;126/366; 219/326 [56] References Cited UNITED STATES PATENTS 2,028,565 1/1936 Rupprieht 62/435 X 2,582,134 1/1952 Kimmelletal. 165/104X 2,893,706 7/1959 Smith 165/108 X 2,578,917 12/1951 Bisch 165/164 X 3,269,385 8/1966 Mitchell et al. 62/52 X 3,319,435 5/1967 Boyd et a1 62/52 Primary Examiner-Albert W. Davis, .1 r. Attorney-Hyer, Eickenroht, Thompson & Turner ABSTRACT: The heater includes a vessel containing a heat transfer fluid and a fire tube located adjacent the bottom to heat the heat transfer fluid. The fluid to be heated flows through a coil located in the vessel above the fire tube but submerged in the heat transfer fluid. The coil encircles two void boxes that occupy a substantial portion of the space in the vessel and reduce the volume of heat transfer fluid required to fill the vessel to a level above the boxes and the coil. The void boxes are spaced apart and positioned relative to the fire tube to cause the heat transfer fluid to flow upwardly between the boxes and downwardly past the coil between the boxes and the walls of the vessel due to the heat convection currents produced by the thermosyphonic effect. When the fluid being heated is a gas and the pressure of the gas is to be reduced, a

choke is located in the coil adjacent its outlet to reduce the pressure after the gas has been heated. This reduces the condensation of liquids and the possibility of their freezing due to the reduction in temperature resulting from the pressure drop across the choke.

R 1 Mm 0 mE 1 5V 3 1m 0 w 6 m I r 8 w L 2 F u 1 vl E H S PATENTEUSEP nan ATTORNEYS PATENTEU-SEP 7 I97! FIG. 3

alsoallol SHEET 2 0F 2 IHIIIIHEHIII Elm co FIG. 5

Lawrence J. Sullivan INVE N TOR ATTORNEYS INDIRECT HEATER This invention relates to indirect heaters generally and, in particular, to indirect heaters where an intermediate fluid is employed to transfer the heat from a heat source to the fluid being heated. Specifically, this invention relates to indirect heaters of the type where the fluid to be heated flows through a coil submerged in the heat transfer fluid, which in turn is contained in a vessel having means to heat the heat transfer fluid.

Indirect heaters of the type to which this invention relates are particularly advantageous where the fluid to be heated is under relatively high pressure and it would be uneconomical to build a vessel having sufficient strength to withstand this pressure. With indirect heaters the fluid to be heated flows through a coil so only the coil need be provided with sufficient strength to withstand the pressure of the fluid being heated. There are other advantages in the use of a heater where the heat is transmitted to the fluid being heated through an intermediate fluid transmitting medium such as water. For example, it practically eliminates local overheating of portions of the coil, which could result in corrosion of the tubes.

In indirect heaters, the heat source, which is usually a fire tube through which hot combustion gases flow, is located adjacent the bottom of the vessel. Since it is a well-known face that heat rises, the coil containing the fluid to be heated is located above the tire tube and the fire tube and coil are submerged in a body ofheat transfer fluid. This fluid is usually a liquid, such as water. With nothing more, the water adjacent the fire tubes will be heated to a temperature higher than the rest, become less dense than the rest, and tend to be forced toward the surface by the denser, cooler water. As the heated water is cooled by the transfer of heat to the fluid in the coil, it will sink and displace the heated fluid adjacent to the firetube.

Thus, flow currents will be established in the heat transfer I fluid. These flow currents are haphazard, however, and inefficient and undesirable.

It is therefore an object of this invention to provide an indirect heater that will produce a predetermined flow pattern in the heat transfer fluid in the heater that provides a very efficient transfer of heat from the heating means to the fluid to be heated.

It is another objectof this invention to provide an indirect heater than employs a minimum volume of heat transfer fluid to thereby reduce the time required to bring the temperature of the heat transfer fluid up to the desired level and if water is the heat transfer fluid to reduce the amount of corrosion inhibitors and the amount of antifreeze required in the heater, when the heater is used in an area where the ambient temperature can drop below the freezing point of water.

It is a further and additional object of this invention to provide such an indirect heater having space occupying members that are positioned to establish the desired direction of flow of heat transfer fluid by the therrnosyphonic effect produced by heating the fluid.

It is another object of this invention to provide an indirect heater to heat high pressure gases to offset the refrigeration effeet on the gases when their pressure is substantially reduced, in which the gases are heated by the heater before their pressures are reduced and then reheated before being discharged from the heater.

These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims.

One embodiment of this invention will now be described in detail in connection with the attached drawings, in which:

FIG. 1 is a side view, partially in section and partially in elevation, of the preferred embodiment of the heater to this invention;

FIG. 2 is an end view of the heater of FIG. 1, this view being also partially in elevation and partially in section, being taken along line 2-2 of FIG. 1;

FIG. 3 is a horizontal sectional view of the heater of FIG. 1

taken along line 33; v

' FIG. 4 is a vertical sectional view of the heater taken of FIG. 1 taken along line 44; and

FIG. 5 is a partial side view of the heater taken along line 55 of FIG. 3 and looking in the direction of the arrows. The heater shown includes vessel 10, which is generally rectangular in vertical cross section as shown in FIG. 4. It includes top 10a, bottom 10b, sides 10c, and 10d. End plates l0e and 10f combine with the top, bottom, and sides to form a vessel capable of holding a body of heat transfer fluid, such as water.

Means are provided to heat the heat transfer fluid. In the embodiment shown, U-shaped fire tube 12 is located adjacent the bottom of vessel 10. Leg 12a of the fire tube is connected at one end to fire box 14. Other leg 12b connects to stack 16. Fire box 14 is conventional and includes burners, flame arresters and other control equipment, such as thermostats, pressure controls, and scrubbers as required to cause hot combustion gases to circulation through the U-shaped fire tube and out stack 16. This control and burner equipment is not shown in the drawings except schematically, since it forms no part of this invention and is conventional firebox apparatus.

According to this invention, a space-occupying member is located in vessel 10 above the heating means for submergence in the heat transfer fluid. The space-occupying member is positioned to cause the heat transfer fluid to flow by thermosyphonic effect up one side of the member and down the other due to the heat currents set up in the fluid by the heating means. In the embodiment shown, two space-occupying members l8 and 20 are employed. These members are elongated, boxlike, structures, generally rectangular, in cross section. Each has a top, bottom and sidewalls that are flat. In the embodiment shown, these members are hollow and the top, bottom sides and end portions of each member are connected together to form a watertight box. The boxes are placed in vessel 10 and occupy a substantial portion of the volume of the vessel that-would otherwise have to filled with heat transfer fluid. Since the temperature of these boxes will increase when the heater is in operation, tubes 22 and 23 are connected to the interior of boxes 18 and 20, respectively, to connect the interior of the boxes with the outside of vessel 10 so that the air in the boxes can expand, when heated, without creating a pressure rise inside the boxes.

Space occupying members or void boxes 18 and 20 are positioned in vessel 10 above the heating means, fir tube 12, The members are parallel to each other and spaced apart to provide verticalpassageway 24 between them.

Conduit means through which the fluid to be heated can flow are located in vessel 10 for submergence in the heat transfer fluid.- In the embodiment shown, elongated tube 29 is formed into coil 30 that encircles void boxes 18 and 20 and is located between the outside walls of the boxes and sidewalls 10c and 10d of the vessel. One end of the tube extends out of the vessel through end plate 10f to provide inlet 32. The other end extends through the same end wall 10f to provide outlet 34.

One common use of indirect heaters of this type is to raise the temperature of natural gas so that the pressure of the gas can be reduced without dropping the temperature of the gas to the point where light hydrocarbons and water vapor contained in the gas will begin to condense. Once condensed, these liquids may freeze and plug up the line or cause other problems in the line downstream of the pressure reducing device, which is usually a choke.

The heater in the embodiment shown is arranged for reducing the pressure of natural gas. Adjacent outlet 34 of coil 30, flow restricting means 36 causes a pressure reduction in the fluid flowing through the coil. In the embodiment shown, the flow restricting means comprises an adjustable choke. An end view of the choke can be seen in FIG. 2 and a side view in FIG. 5. Handle 36!) moves a valve element toward and away from a seat to vary the opening through the choke to provide the desired pressure drop.

Preferably the choke is located with at least that portion of housing 36a, within which the pressure reduction occurs, located inside of vessel to receive the benefit of the heat in the heat transfer fluid in which it is submerged. Curved section 29a of tube 29 connects the downstream end of coil 30 and the choke. To obtain additional benefit from the heat in the heat transfer fluid in the vessel, the choke is located away from outlet 32 far enough to provide one additional coil in tube 29. This coil has one leg 31a that extends lengthwise of vessel 10 along the outside of box 20. It then circles back with leg 31b passing between the void boxes just above the fire tube, as shown in FIG. 4. After the pressure of the gas has been reduced through choke 36, the gas will then travel down the length of vessel 10, through the hot heat transfer fluid, and back again before leaving the heater. This allows the low pressure gas leaving the choke to have its temperature raised again to further insure that preferably the as remains well above the temperature at which light ends and water vapor begin to condense. Scrubber 40 is used to dehydrate gas for use as fuel in fire box 14.

As best shown in FIG. 4 with the void boxes positioned as shown with coil 30 encircling them, the heated heat transfer fluid in the vessel will rise from the vicinity of fire tube 12 and flow upwardly between the void boxes through passageway 24. The fluid will then flow laterally across the top of the boxes and downwardly between the outer walls of the boxes and the sidewalls of the vessel back to the vicinity of the fire tubes. By locating coil 30 between the outer wall of the void boxes and the wall of the vessel, the downward flow of the heat transfer fluid will be increased since it will be giving up heat to the cold fluid flowing through the coil. Thus, a definite flow pattern is established in the heat transfer fluid, which causes the fluid adjacent to the fire tubes to be quickly displaced when it has absorbed the .heat therefrom, which increases substantially the efficiency of the heater to transfer heat.

Automatic controls are available to keep the gas leaving the heater at a preselected temperature and pressure. Such controls would regulate the flow of fuel gas to the firebox and vary the opening through the choke.

From the foregoing description of one embodiment of this invention by way of example it will be seen that his invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus and structure.

The invention having been described, what is claimed is:

1. A heater for transferring heat indirectly from a heat source to a fluid flowing through the heater comprising a ves se] for containing a volume of heat transfer fluid, means positioned adjacent the bottom of the vessel for heating the heat transfer fluid, two generally vertical space occupying members positioned in the vessel above the heating means for submergence in the heat transfer fluid to reduce the volume of such fluid required to submerge the heating means and the space occupying members, said members being in spaced parallel relationship above the heating means with their outer edges spaced apart sufficiently to cause the heat transfer fluid to flow upwardly between the members when heated by the heating means and to flow downwardly between the members and the side of the vessel back to the vicinity of the heating means, and conduit means positioned in the vessel for submergence in the heat transfer fluid for conducting the fluid to be heated through the vessel to absorb heat from the heat transfer fluid, said conduit means comprising an elongated tube coiled around the two space occupying members between the members and the sides and ends of the vessel to absorb heat from and to cool the heat transfer fluid as it flows downwardly between the members and the sides and ends of the vessel to thereby encourage a downward flow of said fluid between the members and the sides of the vessel and said upward flow of the fluid between the members the bottom of each space occupying member is inclined upwardly toward the other to help direct the heat transfer fluid rising from th gicinity of the heating means into the space between the memers 2. The indirect heater of claim 1 in which the space-occupying members are generally rectangular in transverse cross section having tops, bottoms, and sides that are generally flat.

3. A heater for transferring heat indirectly from a heat source to a fluid flowing through the heater comprising a vessel'for containing a volume of heat transfer fluid, means positioned adjacent the bottom of the vessel for heating the heat transfer fluid, two generally vertical space occupying members positioned in the vessel above the heating means for submergence in the heat transfer fluid to reduce the volume of such fluid required to submerge the heating means and the space occupying members, said members being in spaced parallel relationship above the heating means with their outer edges spaced apart sufficiently to cause the heat transfer fluid to flow upwardly between the members when heated by the heating means and to flow downwardly between the members and the side of the vessel back to the vicinity of the heating means, and conduit means positioned in the vessel for submergence in the transfer fluid for conducting the fluid to be heated through the vessel to absorb heat from the heat transfer fluid, said conduit means comprising an elongated tube coiled around the two space occupying members between the members and the sides and ends of the vessel to absorb heat from and to cool the heat transfer fluid as it flows downwardly between the members and the sides and ends of the vessel to thereby encourage a downward flow of said fluid between the members and the sides of the vessel and said upward flow of the fluid between the members, a flow-restricting means in said elongated tube to reduce the pressure of the fluid flowing through the tube, said flow-restricting means being located adjacent the outlet of the tube to cause the reduction of pressure after the fluid has been heated by the heat transfer fluid to reduce the amount of freezing and condensing occurring because of said pressure drop and resulting temperature drop, the portion of the elongated tube between the flow-restricting means and the outlet is positioned to be submerged in the heat transfer fluid in the vessel to heat the fluid downstream of the flow restriction before it leaves the vessel. 

1. A heater for transferring heat indirectly from a heat source to a fluid flowing through the heater comprising a vessel for containing a volume of heat transfer fluid, means positioned adjacent the bottom of the vessel for heating the heat transfer fluid, two generally vertical space occupying members positioned in the vessel above the heating means for submergence in the heat transfer fluid to reduce the volume of such fluid required to submerge the heating means and the space occupying members, said members being in spaced parallel relationship above the heating means with their outer edges spaced apart sufficiently to cause the heat transfer fluid to flow upwardly between the members when heated by the heating means and to flow downwardly between the members and the side of the vessel back to the vicinity of the heating means, and conduit means positioned in the vessel for submergence in the heat transfer fluid for conducting the fluid to be heated through the vessel to absorb heat from the heat transfer fluid, said conduit means comprising an elongated tube coiled around the two space occupying members between the members and the sides and ends of the vessel to absorb heat from and to cool the heat transfer fluid as it flows downwardly between the members and the sides and ends of the vessel to thereby encourage a downward flow of said fluid between the members and the sides of the vessel and said upward flow of the fluid between the members the bottom of each space occupying member is inclined upwardly toward the other to help direct the heat transfer fluid rising from the vicinity of the heating means into the space between the members
 2. The indirect heater of claim 1 in which the space-occupying members are generally rectangular in transverse cross section having tops, bottoms, and sides that are generally flat.
 3. A heater for transferring heat indirectly from a heat source to a fluid flowing through the heater comprising a vessel for containing a volume of heat transfer fluid, means positioned adjacent the bottom of the vessel for heating the heat transfer fluid, two generally vertical space occupying members positioned in the vessel above the heating means for submergence in the heat transfer fluid to reduce the volume of such fluid required to submerge the heating means and the space occupying members, said members being in spaced parallel relationship above the heating means with their outer edges spaced apart sufficiently to cause the heat transfer fluid to flow upwardly between the members when heated by the heating means and to flow downwardly between the members and the side of the vessel back to the vicinity of the heating means, and conduit means positioned in the vessel for submergence in the transfer fluid for conducting the fluid to be heated through the vessel to absorb heat from the heat transfer fluid, said conduit means comprising an elongated tube coiled around the two space occupying members between the members and the sides And ends of the vessel to absorb heat from and to cool the heat transfer fluid as it flows downwardly between the members and the sides and ends of the vessel to thereby encourage a downward flow of said fluid between the members and the sides of the vessel and said upward flow of the fluid between the members, a flow-restricting means in said elongated tube to reduce the pressure of the fluid flowing through the tube, said flow-restricting means being located adjacent the outlet of the tube to cause the reduction of pressure after the fluid has been heated by the heat transfer fluid to reduce the amount of freezing and condensing occurring because of said pressure drop and resulting temperature drop, the portion of the elongated tube between the flow-restricting means and the outlet is positioned to be submerged in the heat transfer fluid in the vessel to heat the fluid downstream of the flow restriction before it leaves the vessel. 